The present invention relates generally to acoustic speakers, and more particularly to sealed speaker systems (also known in the art as acoustic suspension or air suspension speaker systems).
Sealed speaker system designs are based on placing the speaker, particularly the driver (or electroacoustic transducer) at the interface between the open listening space and a substantially closed volume of air at or near ambient barometric pressure. The main functions of the enclosed air volume are to acoustically isolate the rear of the driver from the open listening space, and to provide a controlled restoring force to the speaker's diaphragm.
In a sealed enclosure, as the diaphragm of a speaker driver moves in and out (into and out of the sealed enclosure), the speaker driver causes the volume of air inside the sealed enclosure to be compressed or expanded within the sealed enclosure, and the air outside the sealed enclosure to be compressed or expanded, setting up a sound wave that propagates through the air outside the sealed enclosure. Since no air can enter or leave the sealed enclosure (since it is sealed and because the sealed enclosure has a fixed volume, except for the excursion of the speaker diaphragm, driven by the speaker driver, into and out of the sealed enclosure), the air present in the sealed enclosure must expand to take up more space as the speaker driver moves the speaker diaphragm forward or compress to take up less space as the speaker driver moves the speaker diaphragm backward. The compression and expansion of air inside the sealed enclosure alters the pressure of the air inside the sealed enclosure compared to the ambient air pressure outside the sealed enclosure (very little temperature variation occurs). As air compresses, the air pressure increases. As air expands, the air pressure decreases. These changes in air pressure affect the diaphragm of the speaker driver since it is the only part of the sealed enclosure capable of moving. If the pressure inside the sealed enclosure is greater than the air outside (from the speaker diaphragm moving in), the high internal pressure in the sealed enclosure acts to push the speaker diaphragm out and equalize the internal air pressure with that of the air outside the sealed enclosure. If the pressure inside the sealed enclosure is less than that outside the sealed enclosure, the outside air will act to push the speaker diaphragm back toward the sealed enclosure and increase the inside air pressure, again seeking equalization. Because of the tremendous pressure differentials generated with large speaker diaphragms when such large speaker diaphragms move even a small distance, (relative to the volume of the sealed enclosure) a tremendous force can be required to move large speaker diaphragms in sealed enclosures, unless large volumes of air (relative to the distances the speaker diaphragm will be expected to move and the area of the speaker diaphragm) are contained within the sealed enclosure. Unfortunately, this means that the sealed enclosure must be large in size (or alternatively consume large amounts of power).
In an attempt to maintain low frequency response and to reduce size, open enclosures (i.e., enclosures that are not sealed) employ non-acoustic-suspension system designs having one or more acoustic resonant ports and/or chambers to constructively blend the acoustic energy radiating from the back of the speaker diaphragm with that from the front of the speaker diaphragm. This approach is known in the art as bass reflex. Some open enclosure systems also include one or more passive radiators. Unfortunately, the major disadvantage with these speaker system designs are the grossly nonlinear frequency and phase response resulting from the open enclosure design, and the loss of cone control at frequencies below the design resonance.
Striving for the audible performance advantages of a sealed design, some system designs use a plurality of drivers arranged in various push-pull or sub-chambered configurations in an attempt to overcome the large sealed enclosure required in a sealed enclosure design. These multi-driver arrangements may, on occasion, approximate the frequency response/fidelity behavior of a full-sized sealed enclosure design but at a severe power efficiency penalty.
There is thus a need in the art for a sealed enclosure design for an acoustic suspension speaker system that provides the same desirable fidelity, efficiency and output characteristics of a full-sized sealed enclosure design for an acoustic suspension speaker system without the requirement of a large sealed enclosure.